The sulfur compounds degrade equipment and catalyst used in the processes such as petroleum refining processes and petrochemical processes. Or, sulfur oxides generated during combustion cause inconveniences such as causing acid rain. Therefore, the sulfur compounds are regarded as a problem. In particular, the sulfur compounds contained in raw materials used in the processes are regarded as the problem. Therefore, various methods have been studied to remove the sulfur compounds.
As methods for removing the sulfur compounds contained in the raw materials used in the petroleum refining processes, the petrochemical processes and the like, a method for recovering sulfur from the sulfur compounds decomposed using the catalyst, a method for removing the sulfur compounds adsorbed on the adsorbent, and the like are mainly known.
An example of a method for decomposing the sulfur compounds using the catalyst is a hydrodesulfurization method. In the hydrodesulfurization method, the sulfur compounds are decomposed by hydrogen at a high temperature and in presence of the catalyst. This method is useful as a method for processing the raw materials containing a high concentration of sulfur compounds. However, it is pointed out that the method has problems such as using the equipment for supplying hydrogen, requiring a high temperature of 300 to 400° C., and complicated handling of the catalyst in a catalytic reaction (PATENT LITERATURE 1). In addition, the raw material and hydrogen may also react to each other to produce another compound (byproduct). Therefore, the hydrodesulfurization method also has a problem that it cannot be used in a process that should avoid such a reaction. For these reasons, the hydrodesulfurization method is generally widely used in the petroleum refining processes.
On the other hand, in the method for removing the sulfur compounds adsorbed on the adsorbent, the raw material containing the sulfur compounds flows in a tower filled with the adsorbent under condition of room temperature to 400° C. This method is characterized in that it is simple, need not a hydrogen supply equipment, and can remove the sulfur compounds to the order of ppm or less. Known adsorbents for the sulfur compounds include the adsorbent that physically adsorb the sulfur compounds and the adsorbent that chemically adsorb them. Alumina is known as the physical adsorbent. Among chemical adsorbents, the adsorbent containing zinc oxide is known as the adsorbent used at high temperatures. The adsorbent containing copper oxide is known as the adsorbent that can be used even at room temperature.
However, when processing the raw material containing a high concentration of sulfur compounds, there is a problem that frequency of replacement of the adsorbent increases. In addition, there are also problems such as different adsorptive power depending on the type of sulfur compound. For these reasons, the method using the adsorbent is generally widely used in the petrochemical processes (PATENT LITERATURE 2).
The sulfur compound adsorbent is generally required to have a high sulfur compound adsorption rate and a large sulfur compound adsorption amount. Further, the sulfur compound adsorbent used for industry is also required to have, for example, physical characteristics such as mechanical strength in addition to the above-described chemical characteristics. It is known that the sulfur compound adsorbent having a low mechanical strength is generally easily pulverized and crushed. For example, PATENT LITERATURE 3 discloses that the sulfur compound adsorbent used in a liquid phase is easily crushed, and therefore a high crushing strength of 4 kg or more is required.